In large scale information and communication technology (ICT) systems, such as datacenter networks, optical interconnects, especially silicon photonics, are enabling technologies that offer various advantages such as high bandwidth, high density, compactness, low cost, low power consumption, compatibility with mature CMOS (complementary metal oxide semiconductor) processes, monolithic integration, etc. Grey light (i.e. single wavelength) parallel silicon photonics is highly cost effective for very short reach applications such as chip-to-chip, module-to-module and linecard-to-linecard interconnects. Grey light parallel silicon photonics can extend the reach to kilometers. WDM (wavelength division multiplexing) silicon photonics modules, using multiple wavelength laser arrays at the transmitter side, allow aggregating high speed optical signals into a single optical waveguide and fiber for longer reach interconnects at lower cost.
Despite disparities in requirement and technical implementation, grey light and WDM solutions can coexist to achieve different interconnect scenarios. For example, at the higher hierarchy levels such as the top-of-rack (ToR) and aggregated switches, or the inter-datacenter interconnects, the WDM solution can leverage higher-cost laser chips by using much less fiber (cable) counts and offering all optical passive routing. On the other hand, at the lower level more static point-to-point interconnects, grey light parallel optics is more cost effective and requires lower power budget. The disparity between the parallel and WDM solutions conventionally requires a conversion from single wavelength grey light to multiple wavelengths. Although this operation can be realized with different optical transceiver modules via O-E-O (optical-electrical-optical) two-stage conversion, this process is very costly and the power consumption on the electronics alone is very high, especially for high bit rates in which CDR (clock data recovery) and signal processing and regeneration are necessary.